This invention uses the band of a Rolamite rolling cluster to act as a rolling gate to throttle fluid through a porous passage. The rolling cluster rollers are of sufficient mass so that the vertical component of the force due to gravity provides a constant force bias to the movement of the rolling cluster and therefore the rolling gate band.
The Rolamite is a simple machine which moves without sliding friction. The basic geometry consists of two rollers, a guideway made up of two parallel rolling planes restraining the rollers, the planes being spaced apart a distance less than the sum of the diameters of the rollers, and a resilient band supported under tension between the planes with a portion of the band wrapped partially around the first roller and looped in reverse fashion about the second roller. The portion of the band in contact with the rollers and the rollers themselves will hereinafter be referred to as the rolling cluster.
According to the prior art, rolling tape gates have been used to throttle flow through a high strength porous material. The tape is rolled out on the surface of the porous material and thereby determines the area of the material through which flow will be allowed. In the prior art, the rolling tape is mechanically held at a preselected position for the desired quantity of flow. For example, in U.S. Pat. No. 3,726,313 issued on Apr. 10, 1973 to Pandya, the Rolamite is used as a valve mechanism and the rolling cluster is mechanically restrained at selected positions to valve the fluid. In the aforementioned prior art devices the flow area of the porous passage remains constant irrespective of any change in the external demands on the valve and can be changed only upon physically rolling the tape and fixing it at another desired position.
U.S. Pat. No. 3,794,068 issued on Feb. 26, 1974 to the instant inventor, Richard A. Milroy, disclosed an automatic flow control valve which uses a negator spring to provide a constant force to resist the movement of a rolling cluster of a Rolamite. The result was an automatic volumetric flow control valve. A negator spring is a strip of flat spring stock which is stressed on one side to make it roll upon itself. The unique feature of the negator spring is that the spring force is constant all along its length. As disclosed in the aforementioned patent the valve maintains the flow rate at a constant level since any increase or decrease in the differential pressure across the negator-spring biased rolling cluster will cause a corresponding movement of the rolling cluster, which in turn results in a change in the flow cross- sectional area of the porous passage, until an equilibrium is again reached. Since the bias of the negator-spring is constant all along the length of motion of the rolling cluster, the equilibrium will exist only for the same volumetric flow rate irrespective of pressure changes in the system.